With the global trend of miniaturization, electronic devices are becoming smaller. For semiconductor devices required to operate at high power levels, wafer thinning improves the ability to dissipate heat. As final thickness is decreased, the wafer progressively becomes weaker to support its own weight and to resist the stresses generated by post backgrinding processes. Thus, it is important to reduce the damages caused by backgrinding and improve its quality.
The original thickness of silicon wafers during chip fabrication is 725-680 μm for 8 inch wafers. In order to obtain faster and smaller electronic devices, the wafers need to be thinned before dicing into individual chips. The grinding process consists of two steps. First, a coarse abrasive wheel grinds the surface to around 270-280 μm, but leaves behind a damaged Si surface, the (backside) surface of the Si wafer. Then, a fine abrasive wheel smoothens part of the damaged surface and grinds the wafer to 250 μm. Wafers with thicknesses down to 100-50 μm are virtually a standard requirement for some IC chip applications. For a long time now the most common thickness of about 180 μm in smart cards is being replaced by the thinner and thinner IC chips.
Backgrinding with a metal-bonded superabrasive wheel generally is not advisable due to contamination issues. Circuitries on the front side of the wafer can cause metal interference from the wheels. Therefore, metal-bonded superabrasive wheels should not be employed for backgrinding application. On the other hand, glass bonded superabrasive wheels with the same size grain will induce more subsurface damage and will adversely affect the surface roughness of the finished silicon wafer.
In such situations, resin bonded superabrasive products are preferred. Due to the compliant nature of the bond it will improve surface roughness and induce less subsurface damage. The bond typically will not interfere with the circuitries. Thus, Resin bonded products are best suited for backgrinding applications.
Moreover, superabrasive tools typically must have an open-porous structure in order to minimize accumulation of swarf generated during grinding, and to cool, or at least maintain, a consistent surface temperature at the work piece to which the grinding tool is being applied. Manufacturing a tool that has sufficient strength and wear characteristics, and which also has sufficient porosity, is a persistent challenge, particularly in view of the ever-increasing number of applications to which such tools are being put.
Therefore, a need exists for grinding tools capable of roughing or finishing hard work pieces, as well as for methods of manufacturing such tools, that reduce or eliminate the above-mentioned problems.